Dronedarone, SR 33589, N-[2-Butyl-3-[4-[3-(dibutylamino)propoxy]benzoyl]-5-benzofuranyl]methanesulfonamide, having the formula [1]:
is a drug for the treatment of arrhythmia (U.S. Pat. No. 5,223,510).
A prior art method for preparing dronedarone [1], disclosed in U.S. Pat. No. 5,223,510, starts from 2-butyl-5-nitrobenzofuran according to the following Scheme 1:

The starting material 2-butyl-5-nitrobenzofuran is prepared by multi-stage processes, as showed in Scheme 2 (U.S. Pat. No. 5,223,510, H. R. Horton and D. E. Koshland, J. Methods in Enzymology, 1967, v. 11, 556) and Scheme 3 (WO 01/28974 A2 and WO 01/29019 A1):


It is known that catalytic reduction of 2-butyl-5-nitrobenzofuran (3.4 atm H2/PtO2/EtOH) gives 2-butyl-5-benzofuranamine free base, which reacts with methanesulfonyl chloride in the presence of triethylamine as acid scavenger and carbon tetrachloride as a solvent to give N-(2-butyl-5-benzofuranyl)-N-(methylsulfonyl)methanesulfonamide [14a] instead of N-(2-butyl-5-benzofuranyl)methanesulfonamide [14] (U.S. Pat. No. 5,223,510, Scheme 4):

Compound [14a] may be converted back to [14] but this necessitates the use of larger amounts of methanesulfonyl chloride and of acid scavenger, thus causing increased costs. It also has to be noted that 2-butyl-5-benzofuranamine free base is an unstable compound and can not be stored for long periods of time.